Comparison of PTV based on FDG PET-CT versus 4DCT in non-small cell lung cancer

Objective To compare the positional and volumetric differences of planning target volumes(PTVs)based on fluorodeoxyglucose(FDG)positron emission tomography/computed tomography(PET-CT)and four-dimensional CT (4DCT)for the primary tumor of non-small cell lung cancer(NSCLC) . Methods Fifteen patients with NSCLC sequentially underwent three-dimensional CT (3DCT) , 4DCT, and FDG PET-CT scans of the thorax. IGTV10 was defined on 10 respiratory phases of 4DCT images; IGTVPET was defined on PET-CT images using a fixed threshold of 15% of the maximum standard uptake values. PTV4D and PTVPET were obtained by adding a 10 mm margin around IGTV10 and IGTVPET.The differences in volume, position, and degree of inclusion(DI)between PTVPET and PTV4D were evaluated. Results There was no significant difference in centroid position between PTVPET and PTV4D (P=0.589, 0.147, and 0.096). There was no significant difference in volume between PTVPET and PTV4D (P=0.156) ; however, PET-CT resulted in an >20% change in PTV in 5 of 15 patients, the PTVPET volume increased (average 30%) in 10 patients, and the PTVPET volume decreased (average 11%) in 5 patients. The mean DI of PTV4D in PTVPET was 85%, and 7%-46% of PTVPET was not included within the PTV4D. The DI between PTV4D and PTVPET showed no significant correlation with the 3D motion vector (P=0.134and 0.405) . Conclusions Although there are no significant differences in centroid position and volume between PTVPET and PTV4D for the primary tumor of NSCLC, the spatial mismatch between them is apparent and the mismatch shows no correlation with tumor displacement. Key words: Tomography, positron-emission, fluorodeoxyglucose; Tomography, X-ray computed, four-dimensional; Planning target volume; Degree of inclusion; Lung neoplasms/radiotherapy